A low-cost through via interconnection for ISM WLP

WLP (Wafer level packaging) for image sensor device has the advantage of small size, high performance and low cost. In WLP technology, in order to establish electrical interconnection from image sensor contact pad to the backside of the wafer, several structures have been developed, such as T-contact and TSV (Through Silicon Via). In this paper, a wafer level package of image sensor with new type TSV electrical interconnection for image sensor pad is presented. The target of this development is to reduce process cost and difficulty, and to increase yield of image sensor packaging. Key fabrication processes include glass protecting wafer bonding, device wafer thinning, backside through via etching, via passivation layer deposition, pad oxide opening, via filling and backside re-routing layer formation, etc. Compared to large opening area of tapered via on the backside of CMOS image sensor wafer, only small opening area is needed for making via interconnection with vertical sidewall presented in this paper. A fillet structure at bottom corner of via holes can help to reduce sequent process difficulty, so that low-cost and simplified unit processes are successfully adopted in the fabrication process for through via formation. The through via interconnection shows good electrical connection performance, and high-quality photo images are obtained by packaged image sensor device.